The present invention relates to internal combustion engines and pertains particularly to high compression, high air to fuel burning spark ignition engines.
Heretofore the fuel economy of automobiles has been very poor. This is primarily because of the lack of incentive to develop highly efficient engines because of the abundance of inexpensive fuel such as gasoline. The lack of control over emissions and emission standards has also contributed to the extensive use of inefficient automotive engines.
Recent emission regulations has also resulted in various modifications of automobile engines, which has resulted in a further decrease in fuel economy. These changes have also resulted in loss of power per size of engine, hotter running engines, and thus shorter life, higher fuel consumption, and the requirement for more expensive, higher octane fuels.
Many factors can affect fuel economy either directly or indirectly. Higher compression rations can increase fuel economy, but this is typically offset by mechanical losses and resultant losses from detonation for internal combustion engines. High compression ratios on the order of 12 to 1 for gasoline engines provide optimum fuel economy with the resultant problems, as pointed out above. Diesel engines, on the other hand, can run at higher compression ratios such as 22 to 1, at excellent efficiency and without detonation problems. However, such engines are heavy and extremely expensive for automotive use.
Higher air to fuel ratios can also increase fuel economy. However, current design of gasoline engines provide engines that cannot operate at air to fuel ratios much higher than 18. This is much less than is optimum for best fuel economy. Diesel engines can typically operate well at such high air/fuel ratios because of stratified charge fuel injection. However, the typical gasoline engine operates on a pre-mix of air and fuel, and cannot operate at such high air to fuel ratios.
In gasoline engines the flame of combustion is obtained by heating up the air fuel mixture by means of a spark until it ignites. The turbulence in the air fuel mixture spreads the flame throughout the combustion chamber. Flame propogates more rapidly throughout a low air to fuel ratio than in a high air to fuel ratio.
It has been found that at any air to fuel ratio the flame propagation rate varies directly as engine speed. In other words, if the engine speed is halved the flame propagation is halved also. This is believed to be as a result of the turbulent mass transfer within the cylinder which varies directly with speed. At higher air fuel ratios the flame is slower to propagate and the flame propagation rate varies directly with engine speed. Ignition is difficult at high air fuel ratios and the slow propagation of the flame raises fuel consumption.
In order to gain the fuel economy advantages of burning high air to fuel ratios, the mixture must be burnt much more quickly and at higher air to fuel ratios that is currently obtained. This is also necessary for low emissions and the use of more economic low octane fuels such as diesel oil or kerosene. Most of the combustion must occur immediately after top dead center encompassing a very few degrees of crank rotation. Current engine design is such that high air to fuel burning is so slow when it occurs, that it is still burning in the exhaust, causing overheating of the exhaust valves and the like and destructive to the life of the engine. This also creates detonation, pre-ignition, and wasting of fuel.
The running of an engine on a low air to fuel ratio can result in detonation or auto-ignition of a significant part of the air fuel mixture during propagation of the flame within the combustion chamber. Such detonation or auto-ignition will rapidly damage an engine. A number of things can be done to eliminate or reduce detonation or auto-ignition. For example, a conventional engine can be run at a higher speed with lower throttle to minimize the time needed to overheat and auto-ignite. This, of course, is contrary to the economic lower engine speed wider open throttle operation. The compression ratio can be lowered to reduce gas temperatures and the spark can be retarded, all of which are detrimental to gasoline economy. A high octane fuel can be used which gives a high auto-ignition delay time. These higher octane fuels are obtained at a price by use of lead additives, which becomes a pollutant and destroys exhaust catalyst. High octane unleaded fuels are of course much more expensive and are in short supply.
The typical gasoline engine in an automobile is highly throttled as ordinary operation demands only a small fraction of the maximum power available. This results in a lower air inlet manifold pressure and a much lower pressure than in the exhaust manifold. Such conditions result in exhaust products of the last combustion cycle becoming mixed with the air fuel charge. This dilution of the air fuel mixture results in problems of slow rates of propagation and creates problems of ignition and propagation of the higher air fuel ratios. This problem could be minimized by running the engine at a lower engine speed with a wider throttle opening but this is inhibited by detonation problems of current engines. By use of low air fuel mixture the problem can be minimized, which of course is contrary to good fuel economy. With a closed throttle, even at optimum air fuel ratios, the flame propagation is slow causing hot exhaust, poor economy, and for a vital period, these exhaust products being hot, well above 2000.degree. F., puts heat into the cylinder walls causing difficulty in cooling and detonation and causes a short engine life.
Higher economy is obtained by fast burning of high air fuel ratios and by the use of higher compression ratios. An additional considerable gain could be obtained with the proper combustion chamber design and by the methods of driving.
It is desirable to have a light weight, low bulk, high power engine for automotive use. The light weight and low bulk results in greater gasoline economy, better styling and a more roomy auto with lower manufacturing costs. while the higher power engines is desired, by current consumers, the emission regulations have resulted in detuning of the engines so that they develop less power than former days while engine size and costs have increased.
Accordingly, it is desirable that an engine be available which overcomes the above problems of the prior art.